1. Technical Field
A method for forming a tantalum oxide capacitor is disclosed, and more particularly, a method for forming a tantalum oxide capacitor is disclosed in which tantalum oxide is deposited by an atomic layer deposition (ALD) process so that the step-coverage of the tantalum oxide layer is improved and accordingly the electrical characteristics of the resultant capacitor are improved.
2. Description of the Related Art
In general, a capacitor stores a charge and then supplies the charge required for the operation of a device, such as a semiconductor device. As the integration of the semiconductor devices increases, the size of the cells becomes smaller, and the capacitance required for the operation of the devices increases. The capacitance required in a semiconductor device having a greater integration than 64M DRAM is greater than 30 pF per cell.
Also, as the integration of the semiconductor devices increases, miniaturization of capacitors has been required. However, due to the limitation of the size required in storing a charge to satisfy a required capacitance, difficulties arise in miniaturizing semiconductor capacitors.
The N/O (SiNxOy/SiO2) capacitor, which is in current use, cannot be employed with the next generation DRAM which has an integration of greater than 256M. As a result, a tantalum oxide capacitor has been developed. However, as the aspect ratio increases in the tantalum oxide layer according to the miniaturization of the device, the step-coverage characteristic deteriorates. For example, as the design rule is reduced from 0.16 xcexcm to 0.13 xcexcm, the step-coverage may be reduced from 96% to 73%.
The reduction of the step-coverage may cause deterioration of the electrical properties of the capacitor, which cause reduction of capacitance of the capacitor. Therefore, a capacitance sufficient to operate the semiconductor cannot be secured. Furthermore, if the lower electrode is made of a metal, the tantalum oxide layer may not be deposited evenly due to the roughness of the surface of the metal, so there is a possibility that the tantalum oxide layer will become too thin in some locations. Such a phenomenon causes a leakage current since the electric field is concentrated when a bias is applied.
Due to such a problem of the conventional art, there is a considerable need for forming the tantalum oxide layer uniformly on the lower electrode, to increase the step coverage and prevent the problem of the tantalum oxide layer becoming too thin as a result of the roughness of the underlying metal electrode.
Methods for forming a tantalum oxide capacitor are disclosed, in which tantalum oxide is deposited by an atomic layer deposition ALD process so that the tantalum oxide layer is deposited uniformly on a lower electrode, whereby the step-coverage of the tantalum oxide layer is improved and accordingly the electrical characteristics of the capacitor are improved.
One disclosed method for forming a tantalum oxide capacitor comprises: forming a nitride layer by nitriding an upper part of a lower electrode; depositing a tantalum-nitride Taxe2x80x94N layer on the nitride layer by using an atomic layer deposition ALD method; forming a tantalum oxide layer by oxidizing the tantalum-nitride layer; and forming an upper electrode on the tantalum oxide layer.
As described above, according to one disclosed method for forming a tantalum oxide capacitor, a tantalum-nitride layer is deposited by an atomic layer deposition ALD process and then a tantalum oxide layer is formed by oxidizing the tantalum-nitride layer, and therefore, the step-coverage of the tantalum oxide layer is improved and the electrical characteristics of the capacitor are improved.